Assessment of a low virulence Australian isolate of Anaplasma marginale for pathogenicity, immunogenicity and transmissibility by Boophilus microplus

Bovine Anaplasmosis: Will there ever be an almighty effective vaccine?

Bovine anaplasmosis is a tick-borne bacterial disease with a worldwide distribution and the cause of severe economic losses in the livestock industry in many countries, including México. In the present work, we first review the elements of the immune response of the bovine, which allows ameliorating the clinical signs while eliminating the majority of the blood forms and generating an immunologic memory such that future confrontations with the pathogen will not end in disease. On the other hand, many vaccine candidates have been evaluated for the control of bovine anaplasmosis yet without no commercial worldwide effective vaccine. Lastly, the diversity of the pathogen and how this diversity has impaired the many efforts to control the disease are reviewed.

First report regarding molecular epidemiology and novel variant identification of Anaplasma centrale in cattle from Pakistan

Anaplasma centrale (A. centrale) is an obligate red blood cell residing tick transmitted rickettsiae that has not been studied extensively for its prevalence in cattle along with its epidemiology. Aim of this investigation was to report the seasonal prevalence, phylogeny and epidemiological parameters associated with the prevalence of A. centrale in cattle breeds enrolled from District Layyah in Punjab, Pakistan. A total of 844 blood samples [Cross breed = 300, Holstein Friesian = 244, Sahiwal breed = 300)] were collected from apparently healthy cattle along with epidemiological data during 2017-18. PCR amplified 426 base pair fragment from 16S rRNA gene of A. centrale in 14.4% (122/844) of cattle. Amplified 16S rRNA partial gene sequence of A. centrale were confirmed by DNA sequencing and deposited to GenBank. Highest A. centrale prevalence was observed in spring (24%) followed by autumn (12.4%) summer (10%) and winter (7.1%) seasons. Sahiwal breed (18.3%) was most susceptible to A. centrale infection followed by cross (12.3%) and Holstein Friesian breed (12.3%). 69/844 (8.2%) of Giemsa stained cattle blood smears were also found positive for Anaplasma spp. Farms where animal use to drink pool water and farms where dogs and other dairy animals were living with cattle had higher A. centrale prevalence. Female cattle and dogs having tick burden were found associated with A. centrale infection. Hematological profile was severely disturbed in A. centrale positive cattle. It is recommended that A. centrale should be screened in cattle, in addition to A. marginale, for the effective control of tick born diseases in Pakistan.

Sequence and immunologic conservation of Anaplasma marginale OmpA within strains from Ghana as compared to the predominant OmpA variant

A primary challenge in developing effective vaccines against obligate, intracellular, bacterial tick-borne pathogens that establish persistent infection is the identification of antigens that cross protect against multiple strains. In the case of Anaplasma marginale, the most prevalent tick-borne pathogen of cattle found worldwide, OmpA is an adhesin and thus a promising vaccine candidate. We sequenced ompA from cattle throughout Ghana naturally infected with A. marginale in order to determine the degree of variation in this gene in an area of suspected high genetic diversity. We compared the Ghanaian sequences with those available from N. America, Mexico, Australia and Puerto Rico. When considering only amino acid changes, three unique Ghanaian OmpA variants were identified. In comparison, strains from all other geographic regions, except one, shared a single OmpA variant, Variant 1, which differed from the Ghanaian variants. Next, using recombinant OmpA based on Variant 1, we determined that amino acid differences in OmpA in Ghanaian cattle as compared to OmpA Variant 1 did not alter the binding capacity of antibody directed against OmpA Variant 1, supporting the value of OmpA as a highly conserved vaccine candidate.

Anaplasma ovis as the suspected cause of mortality in a neonatal elk calf

Anaplasma ovis infection is known to occur in elk experimentally, but without clinical signs or significant clinicopathologic changes. An elk farm in southern Indiana experienced the death of 3 neonates. Gross findings suggested hemolytic anemia as the cause of death. Splenic impression smears revealed numerous intra-erythrocytic parasites compatible with Anaplasma spp. Products of a semi-nested PCR targeting the msp4 gene of A. ovis were sequenced and had 100% identity with published A. ovis sequences. Given the clinical presentation, vertical transmission of A. ovis was suspected. Pathologic and molecular findings confirmed that natural A. ovis infection occurred in an elk calf.

Molecular survey and genetic characterization of Anaplasma centrale, A. marginale and A. bovis in cattle from Algeria

Bovine anaplasmosis could be caused by several Anaplasma species. The causative agents are transmitted by ticks and haematophagous arthropods with a high impact on both human and animal health. This study was conducted to estimate the infection rate and to characterize Anaplasma spp. in cattle from Algeria. A molecular survey was performed in Setif district (Northeast Algeria) where a total number of 180 cattle blood samples were collected and tested for the presence of Anaplasma spp. by PCR. Positive samples were genetically characterized based on the 16S rRNA and msp4 genes. PCRs revealed that the infection rates of Anaplasma spp., Anaplasma centrale, Anaplasma marginale and Anaplasma bovis were 42.2%; 39.4%; 11.1% and 4.4%, respectively. All tested animals were negative for A. phagocytophilum. Co-infection occurred in 10% (18/180) of the tested animals, and the most common co-infection pattern was an association between A. centrale and A. marginale (5.5%). Five cattle (2.7%) were co-infected by the three Anaplasma species. Holstein animals (58.1%) were more infected by A. centrale than the other breeds (p = .01). The molecular prevalence of A. centrale was significantly higher in males (54.2%) than in females (34.1%) (p = .001). A. marginale msp4 genetic analysis indicated a high sequence diversity of Algerian strains, suggesting the importation of live cattle from different origins. Phylogenetic analysis of the 16S rRNA gene of A. bovis and A. centrale revealed a low degree of genetic diversity. Our study suggests that different species of Anaplasma are simultaneously present in the Algerian cattle. To the best of our knowledge, this is the first molecular study and genetic characterization of Anaplasma spp. in Algerian cattle.

Anaplasma marginale: Diversity, Virulence, and Vaccine Landscape through a Genomics Approach

In order to understand the genetic diversity of A. marginale, several efforts have been made around the world. This rickettsia affects a significant number of ruminants, causing bovine anaplasmosis, so the interest in its virulence and how it is transmitted have drawn interest not only from a molecular point of view but also, recently, some genomics research have been performed to elucidate genes and proteins with potential as antigens. Unfortunately, so far, we still do not have a recombinant anaplasmosis vaccine. In this review, we present a landscape of the multiple approaches carried out from the genomic perspective to generate valuable information that could be used in a holistic way to finally develop an anaplasmosis vaccine. These approaches include the analysis of the genetic diversity of A. marginale and how this affects control measures for the disease. Anaplasmosis vaccine development is also reviewed from the conventional vaccinomics to genome-base vaccinology approach based on proteomics, metabolomics, and transcriptomics analyses reported. The use of these new omics approaches will undoubtedly reveal new targets of interest in the near future, comprising information of potential antigens and the immunogenic effect of A. marginale proteins.

Subdominant Outer Membrane Antigens in Anaplasma marginale: Conservation, Antigenicity, and Protective Capacity Using Recombinant Protein

Anaplasma marginale is a tick-borne rickettsial pathogen of cattle with a worldwide distribution. Currently a safe and efficacious vaccine is unavailable. Outer membrane protein (OMP) extracts or a defined surface protein complex reproducibly induce protective immunity. However, there are several knowledge gaps limiting progress in vaccine development. First, are these OMPs conserved among the diversity of A. marginale strains circulating in endemic regions? Second, are the most highly conserved outer membrane proteins in the immunogens recognized by immunized and protected animals? Lastly, can this subset of OMPs recognized by antibody from protected vaccinates and conserved among strains recapitulate the protection of outer membrane vaccines? To address the first goal, genes encoding OMPs AM202, AM368, AM854, AM936, AM1041, and AM1096, major subdominant components of the outer membrane, were cloned and sequenced from geographically diverse strains and isolates. AM202, AM936, AM854, and AM1096 share 99.9 to 100% amino acid identity. AM1041 has 97.1 to 100% and AM368 has 98.3 to 99.9% amino acid identity. While all four of the most highly conserved OMPs were recognized by IgG from animals immunized with outer membranes, linked surface protein complexes, or unlinked surface protein complexes and shown to be protected from challenge, the highest titers and consistent recognition among vaccinates were to AM854 and AM936. Consequently, animals were immunized with recombinant AM854 and AM936 and challenged. Recombinant vaccinates and purified outer membrane vaccinates had similar IgG and IgG2 responses to both proteins. However, the recombinant vaccinates developed higher bacteremia after challenge as compared to adjuvant-only controls and outer membrane vaccinates. These results provide the first evidence that vaccination with specific antigens may exacerbate disease. Progressing from the protective capacity of outer membrane formulations to recombinant vaccines requires testing of additional antigens, optimization of the vaccine formulation and a better understanding of the protective immune response.

Genetic Diversity of Tick-Borne Rickettsial Pathogens; Insights Gained from Distant Strains

The ability to capture genetic variation with unprecedented resolution improves our understanding of bacterial populations and their ability to cause disease. The goal of the pathogenomics era is to define genetic diversity that results in disease. Despite the economic losses caused by vector-borne bacteria in the Order Rickettsiales, little is known about the genetic variants responsible for observed phenotypes. The tick-transmitted rickettsial pathogen Anaplasma marginale infects cattle in tropical and subtropical regions worldwide, including Australia. Genomic analysis of North American A. marginale strains reveals a closed core genome defined by high levels of Single Nucleotide Polymorphisms (SNPs). Here we report the first genome sequences and comparative analysis for Australian strains that differ in virulence and transmissibility. A list of genetic differences that segregate with phenotype was evaluated for the ability to distinguish the attenuated strain from virulent field strains. Phylogenetic analyses of the Australian strains revealed a marked evolutionary distance from all previously sequenced strains. SNP analysis showed a strikingly reduced genetic diversity between these strains, with the smallest number of SNPs detected between any two A. marginale strains. The low diversity between these phenotypically distinct bacteria presents a unique opportunity to identify the genetic determinants of virulence and transmission.

Molecular epidemiology of bovine anaplasmosis with a particular focus in Mexico

Bovine anaplasmosis, caused by the rickettsia Anaplasma marginale, has a worldwide distribution and is the cause of great economic losses in developing countries where it is highly endemic. Transmission is carried mainly by ixodid ticks: Dermacentor spp. and Rhipicephalus (Boophilus) spp. Mechanical transmission is important in disseminating the disease within and across herds. The relationship between the rickettsia, the host and the vector is complex. Several surface proteins (Msps) have been described with functions that span from adhesins towards the erythrocyte and tick cells to evasion of the immune system of the host through the generation of antigenic variants. Biologic transmission of A. marginale through Dermacentor ticks has been well studied but many questions are unresolved as to how this organism spreads within and across herds and little is known about the role Rhipicephalus (Boophilus) ticks play in transmission in the Americas. Mechanical transmission in the absence of ticks and lack of transmission through ticks are questions that need to be addressed. Phylogenetic studies of the rickettsia show wide antigenic and genetic mosaics which affects the design of new vaccines. In the present work we will discuss the molecular elements in the relationship between the rickettsia, the tick and the mammalian host associated to the distribution and persistence of the pathogen in nature.

Anaplasma marginale Yucatan (Mexico) Strain. Assessment of low virulence and potential use as a live vaccine

Anaplasma marginale Yucatan strain was found to have low virulence in cattle. We studied the virulence of this isolate by experimental inoculation of 113 susceptible cattle at increasing doses, after which only one animal required treatment for clinical disease. Subsequently, 104 cattle received a live vaccine of this strain by inoculation, which induced immunoprotection after heterologous challenged exposure with a different A. marginale isolate. In this study 14% of the immunized cattle required treatment as compared with the control nonimmunized cattle, in which 56% required treatment. The A. marginale vaccine strains used for the immunization studies had MSP1a variable regions that were different from those used for the challenge exposure.

Duplex Real-Time Polymerase Chain Reaction for Simultaneous Detection and Quantification of Anaplasma Marginale and Anaplasma Centrale

Anaplasma marginale and Anaplasma centrale are rickettsial pathogens responsible for acute disease and mild infections, respectively, in cattle herds. A duplex real-time polymerase chain reaction (PCR) assay with probes labeled with different fluorophores was developed for simultaneous detection and quantification of A. marginale and A. centrale DNA in bovine blood samples. The assay was able to detect as few as 101 and 102 DNA copies for A. marginale and A. centrale, respectively, with optimal specificity and reproducibility. Analysis by real-time and nested PCR carried out on 54 samples previously tested by reverse line blot hybridization showed that the established duplex real-time PCR assay can detect and quantify the 2 Anaplasma spp., even if present simultaneously in the same blood samples. Such an assay could be used in pathogenesis studies on bovine acute anaplasmosis.

Serological survey of Babesia bovis, Babesia bigemina, and Anaplasma marginale antibodies in cattle from the semi-arid region of the state of Bahia, Brazil, by enzyme-linked immunosorbent assays

The objectives of this work were to determine the prevalence of Babesia bovis, Babesia bigemina, and Anaplasma marginale detecting antibodies in cattle raised in the semi-arid region of the state of Bahia, Brazil, through indirect enzyme linked immunosorbent assays (ELISA) and to compare the performances of indirect enzyme-linked immunosorbent assays with crude (I-ELISA-CrAnaAg) and recombinant major surface protein-5 (I-ELISA-MSP-5Ag), as antigens to detect antibodies against A. marginale. An stable enzootic area was found in Senhor do Bonfim and Euclides da Cunha for B. bovis that showed 86 and 95.5% of prevalence, respectively, and for B. bigemina with 90.8 and 91.3%. On the other hand, Uauá and Juazeiro, were characterized as enzootically unstable areas, since prevalences were: B. bovis--63.7 and 56.4% and B. bigemina--53 and 54.8%, respectively. The prevalence of A. marginale in the four municipalities was above 97% with I-ELISA-CrAnaAg and 94.8% with I-ELISA-MSP-5Ag which is an indication of stable enzootic condition for the rickettsia. The I-ELISA-CrAnaAg and I-ELISA-MSP-5Ag showed a highly significant association (r = 0.977), which means that both ELISA tests are suitable for epidemiological studies of A. marginale.

Genetic diversity of anaplasma species major surface proteins and implications for anaplasmosis serodiagnosis and vaccine development

The genus Anaplasma (Rickettsiales: Anaplasmataceae) includes several pathogens of veterinary and human medical importance. An understanding of the diversity of Anaplasma major surface proteins (MSPs), including those MSPs that modulate infection, development of persistent infections, and transmission of pathogens by ticks, is derived in part, by characterization and phylogenetic analyses of geographic strains. Information concerning the genetic diversity of Anaplasma spp. MSPs will likely influence the development of serodiagnostic assays and vaccine strategies for the control of anaplasmosis.